Low-profile color-mixing lightpipe

ABSTRACT

In one aspect, a light-mixing system is disclosed, which includes a light pipe having an input surface configured for receiving light from a light source, a light-mixing segment optically coupled to the input surface, and an output surface optically coupled to said light-mixing segment through which light exits the light pipe. A putative vector normal to at least one of the input or the output surface forms a non-zero angle relative to a longitudinal axis of the light-mixing segment. In some embodiments, the non-zero angle can be, for example, about 90 degrees.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and is a continuation of U.S.application Ser. No. 16/021,942, filed on Jun. 28, 2018, the teachingsof which are incorporated herein by reference in its entirety.

BACKGROUND

The present invention is generally directed to light-mixing systems formixing light from one or more light sources.

A variety of light-mixing optical systems are available for mixing lightfrom one or more light sources, e.g., solid-state light emitting diodes(LEDs). Some conventional light-mixing systems include one-piececollimators as well as two-piece systems, which can consist of acolor-mixing rod and a secondary lens that is capable of generatingvariable beam angles. As the length of the rod increases, so does theeffectiveness of the light mixing (color mixing) provided by the rod.However, in conventional systems, an increase in the length of themixing rod results in a concomitant increase in the height of thesystem. Many applications, however, require not only excellent lightmixing but also a shorter system height than that provided byconventional systems.

Accordingly, there is a need for improved light-mixing systems.

SUMMARY

In one aspect, a light-mixing system is disclosed, which includes alight pipe having an input surface configured for receiving light from alight source, a light-mixing segment optically coupled to the inputsurface, and an output surface optically coupled to said light-mixingsegment through which light exits the light pipe. A putative vectornormal to at least one of the input or the output surface forms anon-zero angle relative to a longitudinal axis of the light-mixingsegment. In some embodiments, the non-zero angle can be, for example,about 90 degrees.

In some embodiments, the light-mixing system can further include areflective surface that is optically coupled to the input surface andthe light-mixing segment of the light pipe for directing at least aportion of the light received via the input surface to the light-mixingsegment. In some embodiments, the reflective surface is metalized tocause the reflection of the light incident thereon. In otherembodiments, the reflective surface can reflect the light incidentthereon via total internal reflection.

In some embodiments, the light-mixing segment has a polygonal crosssectional profile. By way of example, the light-mixing segment can havea square, a rectangular, a hexagonal, or an octagonal profile.

In some embodiments, the output surface of the light pipe can include aplurality of microlenses, surface texturing or both. By way of example,the surface texturing can be characterized by a plurality of surfaceprojections having a height in a range of about 0.01 mm to about 1 mm.The microlenses can have spherical or aspherical shapes.

In some of the above embodiments, a ratio of a vertical separation (D)between the input and output surfaces of the light pipe relative to alateral separation (L) therebetween can be, for example, in a range 0 toabout 1.

In a related aspect, a light-mixing system is disclosed, which includesa light pipe comprising an input surface for receiving light from alight source, a light-mixing segment optically coupled to the inputsurface, and an output surface that is optically coupled to thelight-mixing segment and through which light can exit the light pipe. Atleast one of the input and output surfaces is positioned relative to thelight-mixing segment such that a resultant propagation direction oflight entering the light pipe via the input surface or exiting the lightpipe via the output surface forms a non-zero angle relative to aresultant propagation direction of light passing through at least aportion of the light-mixing segment.

In another aspect, a light-pipe is disclosed, which includes a curvedlight-guiding waveguide extending from a proximal end to a distal end.The curved light-guiding waveguide can include an input surface at theproximal end configured to receive light from a light source and anoutput surface at the distal end through which light exits thewaveguide. In some such embodiments, a projection lens can be opticallycoupled to the output surface of the light pipe. Further, in someembodiments, the light source can be positioned relative to the inputsurface of the light pipe such that the light entering the input surfacepropagates along a direction opposite to the direction of the lightexiting the output surface.

In some embodiments of the above light-pipe, a putative vector normal tothe input surface of the light pipe is substantially parallel to aputative vector normal to its output surface.

In some embodiments, the curved light-guiding waveguide has a serpentineshape. In some embodiments, the curved light-guiding waveguide has ahemispherical shape.

In some embodiments, the output surface of the light pipe can include aplurality of microlenses and/or surface texturing, such as thosediscussed herein, for diffusing and/or redirecting the light passingthrough the output surface.

In some embodiments, a light mixing system according to the presentteachings can include a heat sink that is thermally coupled to a lightsource of the light mixing system for removing heat therefrom. By way ofexample, the heat sink can include a plurality of fins for facilitatingthe removal of heat from the light source.

In some embodiments, a light mixing system according to the presentteachings can include a light pipe that extends from an input surface toan output surface, where the input and output surfaces are oriented at a90-degree angle relative to one another. In some such embodiments, theoutput surface can include a plurality of microlenses and/or surfacetexturing.

In some embodiments, a light mixing system according to the presentteachings can include a light pipe that extends from an input surface toan output surface, where the input and the output surfaces are orientedat 45 degrees relative to one another. In some such embodiments, theoutput surface can include a plurality of microlenses and/or surfacetexturing.

In some embodiments, a light pipe of a light-mixing system according tothe present teachings can exhibit a tapered cross section extending fromits input surface to its output surface, e.g., the tapered cross-sectioncan result in an increase in the cross-sectional area of the light pipeas the light pipe extends from its input surface to its output surface.

In some embodiments, a light pipe of a light-mixing system according tothe present teachings can have a light pipe exhibiting differentcross-sectional shapes along its length. For example, the cross sectionsof different sections of the light pipe can have different polygonalshapes. Alternatively, in some embodiments, a portion of the light pipe,e.g., a portion proximate to the input surface, can have a polygonalshape and another portion of the light pipe, e.g., a portion proximateto the output surface, can have a round shape.

In the above embodiments, the light pipe and/or the projection lens canbe made of a variety of suitable materials, such as polymeric materials.Some examples of suitable materials include, without limitation, PMMA(polymmethyl methacrylate), silicone, and glass.

Further understanding of various aspects of the invention can beobtained by reference to the following detailed description inconjunction with the associated drawings, which are described brieflybelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically depicts a light-mixing system according to anembodiment,

FIG. 1B is a schematic perspective view of the light pipe employed inthe light-mixing system of FIG. 1A,

FIG. 1C schematically depicts an output surface of an implementation ofthe light pipe of the system shown in FIGS. 1A and 1B, where the outputsurface includes a plurality of microlenses,

FIG. 1D schematically depicts an output surface of an implementation ofthe light pipe of the system shown in FIGS. 1A and 1B, where the outputsurface includes surface texturing,

FIG. 1E schematically depicts an output surface of an implementation ofthe light pipe of the system shown in FIGS. 1A and 1B, where the outputsurface includes both microlenses and surface texturing,

FIG. 1F schematically depicts an output surface of a light pipe of alight-mixing system according to an embodiment, where the output surfacecomprises a plurality of microlenses

FIG. 1G schematically depicts an output surface of a light pipe of alight-mixing system according to an embodiment, where the output surfacecomprises a plurality of microlenses having textured surfaces,

FIG. 1H schematically depicts an output surface of a light pipe of alight-mixing system according to an embodiment, where the output surfacecomprises surface texturing,

FIG. 1J schematically depicts an implementation of the light-mixingsystem of FIG. 1A in which a projection lens is optically coupled to anoutput surface of the system's light pipe,

FIG. 1K schematically depicts a zoom lens employed as a projection lensin an embodiment of a light-mixing system according to the presentteachings, where the zoom lens comprises two lens (the zoom lens isdepicted in a narrow-beam configuration in this figure),

FIG. 1L schematically depicts the zoom lens of FIG. 1K in a wide-beamconfiguration,

FIG. 1M schematically depicts an implementation of the light-mixingsystem of FIG. 1A in which a single-lens zoom lens is employed in anarrow beam configuration,

FIG. 1N schematically depicts the zoom lens of FIG. 1M in a wide-beamconfiguration,

FIG. 2 schematically depicts an array of light-mixing systems accordingto the present teachings,

FIGS. 3A and 3B schematically depict a light-mixing system according toanother embodiment,

FIG. 4A is a schematic perspective view of a light-mixing systemaccording to another embodiment of the present teachings,

FIG. 4B is a schematic cross-sectional view of the light-mixing systemdepicted in FIG. 4A,

FIG. 4C is a schematic view of an implementation of the light-mixingsystem of FIG. 4A in which a portion of the light pipe is positionedvertically below the surface of the light source,

FIG. 4D is a cross-sectional view of the light-mixing system depicted inFIG. 4C,

FIG. 4E is a perspective schematic view of an implementation of thelight-mixing system of FIG. 4C in which a heat sink is coupled to be thelight source,

FIG. 4F is a cross-sectional schematic view of the light-mixing systemdepicted in FIG. 4E with the addition of a projection lens opticallycoupled to the output surface of the light pipe,

FIG. 5A is a schematic perspective view of a light-mixing systemaccording to another embodiment of the present teachings,

FIG. 5B is a schematic cross sectional view of the light-mixing systemdepicted in FIG. 5A,

FIG. 5C is another schematic view of the light-mixing system depicted inFIG. 5A,

FIG. 5D is another schematic view of the light-mixing system depicted inFIG. 5A,

FIG. 5E schematically depicts an embodiment of the light-mixing systemof FIG. 5A in which a heat sink is thermally coupled to the lightsource,

FIG. 5F is another schematic view of the light-mixing system of FIG. 5E,

FIG. 6A is a schematic view of a light-mixing system according toanother embodiment of the present teachings,

FIG. 6B is a schematic view of another implementation of thelight-mixing system depicted in FIG. 6A,

FIG. 6C is a schematic view of an embodiment of the light-mixing systemof FIG. 6A in which a heat sink is thermally coupled to the lightsource,

FIG. 6D is another schematic view of the light-mixing system depicted inFIG. 6C,

FIG. 6E is a schematic view of an embodiment of the light-mixing systemof FIG. 6A in which a projection lens is optically coupled to the outputsurface of the light pipe,

FIG. 7 is a schematic view of a light-mixing system according to anotherembodiment of the present teachings,

FIG. 8A is a schematic view of a light system according to an embodimentin which the input and output surface are oriented at a 90-degree anglerelative to one another,

FIG. 8B is a perspective schematic view of the light system depicted inFIG. 8A,

FIG. 8C is another perspective schematic view of the light systemdepicted in FIG. 8A, illustrating a plurality of microlenses that areoptically coupled,

FIG. 8D schematically depicts an embodiment of the light system shown inFIG. 8A in which a heat sink in thermally coupled to a light sourceproviding light to the light pipe of the light system,

FIG. 8E is a cross-sectional schematic view of the light systemillustrated in FIG. 8D,

FIG. 8F schematically illustrates a light system according to anembodiment in which a projection lens is optically coupled to an outputsurface of a light pipe of the light system,

FIG. 8G is a perspective schematic view of the light system depicted inFIG. 8F,

FIG. 9A is a schematic cross-sectional view of a light system accordingto an embodiment in which the input and output surfaces of a light pipeof the light system are oriented at a 45-degree angle relative to oneanother,

FIG. 9B is a schematic perspective view of the light system illustratedin FIG. 9A, depicting a plurality of microlenses optically coupled tothe output surface of the light pipe of the light system,

FIG. 9C is another schematic perspective view of the light system shownin FIG. 9A,

FIG. 9D is a schematic perspective view of an embodiment of the lightsystem illustrated in FIG. 9A in which a heat sink is thermally coupledto a light source of the light system,

FIG. 9E is a schematic cross-sectional view of the light system shown inFIG. 9D,

FIG. 9F is a schematic view of an embodiment of the light system of FIG.9A in which a projection lens is optically coupled to the output surfaceof a light pipe of the light system, and

FIG. 9G is a schematic perspective view of the light system depicted inFIG. 9F,

FIG. 10 schematically depicts a light pipe having a tapered crosssection exhibiting a progressively increasing surface area from itsinput surface to its output surface, and

FIG. 11 schematically depicts a light pipe for use in a light-mixingsystem according to the present teachings, which exhibits differentcross-sectional shapes along its length.

DETAILED DESCRIPTION

The present invention is generally directed to light-mixing systems thatemploy a light pipe for mixing light received from one or more lightsources. As discussed in more detail below, the light-mixing systemsaccording to the present teachings can provide efficient light mixingwhile having a height that is significantly shorter than that ofconventional light-mixing systems providing comparable light-mixingefficiency.

Various terms are used herein consistent with their ordinary meanings inthe art. By way of clarification, certain terms are further describedbelow.

An input surface is laterally separated from an output surface when twoputative lines, each of which is normal to the center of one of thosesurfaces, are not co-extensive (i.e., they are not superimposed on oneanother).

The “lateral separation” or “lateral distance” between an input surfaceand an output surface of a light pipe refers to the shortest distancebetween two putative vectors normal to the centers of those surfacesalong a direction normal to at least one of those vectors.

The “vertical separation” or “vertical distance” between an inputsurface and an output surface refers to the shortest distance betweenthose surfaces along a direction parallel to a putative vector normal toat least one of those surfaces.

FIGS. 1A, 1B, 1C and 1D schematically depict an optical system 10according to an embodiment of the present teachings, which includes alight pipe 12 that is optically coupled to a light source 14. In thisembodiment, the light source 14 is a multi-color light emitting device(LED), such as an RGBW LED. In other embodiments, other light sources,including single-color LEDs can also be employed.

The light pipe 12 includes an input surface 16 that is positioned inproximity of the light source 14 so as to receive at least a portion ofthe light emitted by the light source 14. In some embodiments, the inputsurface 16 is configured and positioned relative to the light source 14such that it receives at least about 70 percent, or at least about 80percent, or at least about 90 percent, and preferably 100 percent, ofthe light energy generated by the light source.

The light pipe 12 further includes a light-guiding (herein also referredto as light-mixing) segment 20 that extends from a proximal end (PE) toa distal end (DE) and is optically coupled to the input surface 16 toreceive at least a portion of the light entering the light pipe via theinput surface. More specifically, in this embodiment, the light pipe 12includes a reflective surface 22 that is positioned at a 45-degree anglerelative to the input surface 16 for directing the light received viathe input surface 16 into the light-mixing segment 20. In thisembodiment, the reflective surface 22 is metalized. For example, a layerof a suitable metal 22 a, such as gold or silver, can be deposited onthe surface 22 so as to reflect the light incident thereon. In someembodiments, the thickness of such a metal layer can be, for example, ina range of about a few angstroms to about a few microns. In otherembodiments, the reflective surface 22 can be configured so as toreflect the light incident thereon via total internal reflection.

As shown schematically in FIG. 1C, in this embodiment, the input surface16 is positioned relative to the light-mixing segment 20 such that aputative vector (A) normal to the input surface is substantiallyorthogonal to a longitudinal axis (LA) of the light-mixing segment 20.

In many embodiments, the light-mixing segment 20 has a polygonalcross-sectional shape, though cylindrical light-mixing segments can alsobe employed in some embodiments. In this embodiment, the light-mixingsegment 20 includes four peripheral surface portions 20 a, 20 b, 20 c,and 20 d (herein collectively referred to as peripheral surface portions21) that impart a square cross-sectional shape to the light-mixingsegment 20. In this embodiment, these peripheral surface portions areconfigured to reflect light incident thereon via total internalreflection. In other embodiments, one or more of these surface portionscan be metalized for reflecting light incident thereon. In thisembodiment, the input surface 16 is contiguous with the peripheralsurface portion 20 b.

The light entering the light-mixing segment can undergo multiplereflections at surface portions 21 and advance along the light-mixingsegment from the input surface 16 to reach a reflective surface 26disposed at the distal end of the light-mixing segment 20, whichreflects the light incident thereon onto an output surface 24. In thisembodiment, the distal reflective surface 26 can be metalized. Forexample, the reflective surface 26 can be coated with a metal layer 26 ahaving a thickness, for example, in a range of about a few angstroms toabout a few microns. Similar to the input surface, the output surface 24is also positioned relative to the light-mixing segment 20 such that aputative vector (B) normal to the output surface forms a non-zero anglerelative to the longitudinal axis (LA) of the light-mixing segment 20.In this embodiment, this non-zero angle is about 90 degrees. Further, inthis embodiment, the output surface 24 is contiguous with the peripheralsurface portion 20 c.

Further, in this embodiment, a plurality of microlenses 30 are opticallycoupled to the output surface so as to diffuse and/or redirect the lightexiting the optical system via the output surface 24. In thisembodiment, the output surface 24 incorporates the microlenses 30. Inother embodiments, the microlenses 30 can be formed in a separatesubstrate (not shown), e.g., a plastic substrate, which can be coupledto the output surface 24.

As shown schematically in FIGS. 1E and 1F, the microlenses 30 can have avariety of different sizes. By way of example, in some embodiments, themicrolenses can have hemispherical shapes (See, e.g., FIG. 1D) with adiameter in a range of about 0.05 mm to about 1 mm. Further, in someembodiments, the pitch of the microlenses, i.e., the center-to-centerspacing of the microlenses, can be, for example, in a range of about 0.1mm to about 1 mm, e.g., in a range of about 0.1 mm to about 0.5 mm. Insome embodiments, the microlenses can have an aspheric shape.

As shown schematically in FIG. 1G, in some embodiments, the surfaces ofthe microlenses 30 can be textured. For example, the surfaces of themicrolenses 30 can include a plurality of projections 42 having aheight, for example, in a range of about 0.01 mm to about 1 mm.

Further, as shown schematically in FIG. 1H, in some embodiments, theoutput surface can include texturing, e.g., a plurality of projections43 having a height in a range of about 0.01 mm to about 1 mm, withoutmicrolenses.

Referring again to FIG. 1A, in this embodiment, a lateral separation (L)between the input and output surfaces can be, for example, in a range ofabout 20 mm to about 200 mm and a vertical separation (D) between thosesurfaces can be, for example, in a range of about 0 to about 20 mm.Further, the ratio of D/L can be in a range of about 0 to about 1, e.g.,in a range of about 0.1 to about 0.5.

As shown in FIG. 1J, in some embodiments, a projection lens 11 can beoptically coupled to the output surface 24 for projecting the lightexiting the output surface 24 onto a target surface. In someembodiments, the lens 11 is in the form of a zoom lens assembly. Inother embodiments, the optical system may not include a projection lens.

By way of example, FIGS. 1K and 1L schematically depict a zoom lenssystem 13 (herein also referred to as a doublet zoom) that includes alens 13 a providing a positive optical power and a lens 13 b providing anegative optical power. At least one of the lenses, and in some casesboth, is axially movable relative to the output surface of the lightpipe to change the angular spread of the output beam between anarrow-beam spread (shown in FIG. 1K) and a wide-beam spread (shown inFIG. 1L). For example, the angular spread of the output beam can bevaried between about 5 degrees to about 80 degrees. The use of a doubletlens system with one positive lens and one negative lens can beadvantageous in applications where a wide beam range, e.g., divergence(FWHM) in a range of about 20 to about 80 degrees, is required. Inembodiments in which the zoom lens includes a single positive lens(herein also referred to as a singlet zoom), in the “infrafocalposition” (i.e., when the lens is placed close to the output surface ofthe light pipe), the positive power of the lens can reduce thedivergence of the beam exiting through the output surface of the lightpipe (See, FIGS. 1M and IN for schematic representation of a narrow-beamand wide-beam spread of the output beam in a system in which a singletzoom 15 is employed). In contrast, the positive and negative opticalpowers of the lenses of a doublet zoom allow achieving much wider beamspread, e.g., in a range of about 20 degrees to about 80 degrees (FWHM),when the zoom system is in the “intrafocal position.” Further, in manyembodiments, a multiple-lens zoom lens can provide other advantages,such as conventional advantages known in the art.

In some embodiments, the projection lens 11 can be a stationary lensthat receives light emitted by the output surface of the light pipe andprojects that light onto a target surface.

In some implementations, the light system 10 can transfer light from itsinput surface to its output surface with an efficiency in a range ofabout 30% to about 50%.

The light system 10 can provide a number of advantages. For example, itcan provide excellent light mixing while having a significantly shorterheight. In other words, while the length L of the light pipe can besufficiently long so as to cause a desired degree of light mixing, theseparation D between the input and output surfaces can be made muchshorter than that in conventional systems.

With reference to FIG. 1B, in use, the light rays emitted by the lightsource 14, such as the exemplary light rays 1, 2, 3 are incident on theinput surface 16 and enter the light pipe via the input surface. Thereflective surface 22 redirects these light rays into the light-mixingsegment 20. The rays undergo multiple reflections at the surfaceportions 21 to reach the reflective surface 26 at the distal end of thelight-mixing segment. The rays are then reflected at this reflectivesurface 26 to reach the output surface 24. In this embodiment, theresultant propagation direction of the light rays incident on the inputsurface, as characterized, e.g., by the direction of the sum of thevectors associated with the incident light rays (i.e., the direction ofthe central ray 2 in this embodiment) is orthogonal to the resultantpropagation direction of the light rays through the light-mixing segment20 (in this case along the longitudinal axis (LA) of the light-mixingsegment). Similarly, the resultant propagation direction of the lightrays exiting the light pipe via the output surface 24 (i.e., rays 1′, 2′and 3′) is orthogonal to the resultant propagation direction of thelight rays traversing the light-mixing segment 20. In other embodiments,the input and output surfaces can be configured such that the resultantpropagation directions of the light rays entering or exiting the lightpipe can make non-zero angles other than 90 degrees relative to thelongitudinal direction of the light-mixing segment 20.

FIG. 2 schematically depicts a light array 200 that is formed by usingfour of the light-mixing systems 10 discussed above. More specifically,the light array 200 includes light-mixing systems 200 a, 200 b, 200 c,and 200 d, where the light pipes of the light mixing system 200 a issubstantially parallel to the light pipe of the light-mixing system 200c and the light pipe of the light-mixing system 200 b is substantiallyparallel to the light pipe of the light-mixing system 20 d. Further, thepair of light mixing systems (200 a/200 c) are substantially orthogonalto the pair of light mixing systems (200 b/200 d). In some embodimentsof the light array 200, the light-mixing systems 200 a, 200 b, 200 c,and 200 d can be positioned relative to one another such that the outputlight of the systems at least partially overlap when projected onto adesired target.

FIGS. 3A and 3B schematically depict another embodiment 300 of a lightmixing system according to the present teachings. The light-mixingsystem 300 is similar to the light-mixing system 10 discussed aboveexcept that the light pipe 302 employed in this system has an octagonalcross-sectional shape. Further, an output surface 304 of thelight-mixing system 300 is disposed at the end of a segment 306 thatprotrudes above a light mixing segment 308 of a light pipe 302 of thelight-mixing system. Similar to the previous embodiment, thelight-mixing system 300 can include a plurality of microlenses and/orsurface texturing 310 for diffusing and/or redirecting the light exitingthe output surface 304. The light-mixing system 300 can optionallyinclude a projection lens (not shown), such as a zoom lens, that can beoptically coupled to the microlenses/surface texturing 310.

FIGS. 4A and 4B schematically depict another embodiment 400 of alight-mixing system according to the present teachings, which includes alight source 402 and a light pipe 404 to which the light source isoptically coupled. The light pipe 404 has a curved profile and extendsfrom an input surface 406 to an output surface 408. More specifically,in this embodiment, the light pipe 404 has a serpentine shape. Similarto the previous embodiment, the light source 402 is a multi-color LED,though other light sources can also be employed.

In this embodiment, the serpentine-shaped light pipe 404 includessurface portions 404 a, 404 b, 404 c, and 404 d (herein collectivelyreferred to as surface portions 405) that are arranged to impart asquare cross-sectional shape to the light pipe. The light emitted by thelight source 402 enters the light pipe via the input surface 406 andundergoes total internal reflection at the peripheral surface portions405 of the light pipe, thereby advancing along the light pipe to reachthe output surface 408 through which the light exits the light pipe.

A plurality of microlenses 410 are coupled to the output surface 408 fordiffusing and/or redirecting the light exiting through the outputsurface. In this embodiment, the microlenses are implemented as aseparate unit (e.g., in a plastic substrate), which is attached to theoutput surface of the light pipe. In other embodiments, the outputsurface itself can carry the microlenses. In addition or alternatively,the output surface 408 can include surface texturing, such as thatdiscussed above in connection with the previous embodiments.

With continued reference to FIGS. 4A and 4B, the input surface 406 andthe output surface 408 are laterally separated from one another by adistance L and are vertically separated from one another by a distanceD. In this embodiment, the ratio of D to L (D/L) can be, for example, ina range of 0 to about 1. In some embodiments, the lateral distance L canbe, for example, in a range of about 20 mm to about 200 mm and thevertical distance D can be, for example, in a range of 0 to about 20 mm.

As shown schematically in FIGS. 4C and 4D, in some embodiments, aportion of the light pipe 404 can be vertically below the surface of thelight source 402. While in this embodiment, the height of the outputsurface 408 relative to the lowest point of the light pipe is greaterthan the height of the input surface 406, in other embodiments, thelight pipe can be curved such that the height of the output surface 408is less than that of the input surface 406.

With reference to FIGS. 4E and 4F, in some embodiments, a heat sink 411can be coupled to the light source 402 to facilitate removal of heatfrom the light source. In this embodiment, the heat sink 411 includes aplurality of fins 411 a that provide an increased surface area fromwhich the heat generated by the light source can be efficientlydissipated into the external environment. In this embodiment, the heatsink 411 includes an opening 411 b that accommodates a portion of thelight pipe 404 that is positioned vertically below the light source 402.

As shown schematically in FIG. 4F, in some embodiments, a lens 412 canbe optically coupled to the microlenses 410 to receive the light exitingthe light pipe 400, e.g., to project the light onto a target surface. Insome embodiments, the lens 412 can function as a zoom lens. The use of acurved light pipe can provide certain advantages. For example, it canallow efficient light mixing by increasing the path length of the lightthrough the light pipe while ensuring that the height of the system,which can be characterized by the vertical separation D between theinput and output surfaces, is significantly less than the height of aconventional system providing the same degree of light mixing.

FIGS. 5A, 5B, 5C, 5D schematically depict a light-mixing system 500according to another embodiment, which includes a hemispherically-shapedlight pipe 502 that extends from an input surface 502 a to an outputsurface 502 b. In this embodiment, the hemispherically-shaped light pipe502 includes four peripheral surfaces, such as surfaces 503 a, 503 b,and 503 c (the surface opposed to the surface 502 c is not visible inthis figure), which are herein referred to collectively as peripheralsurfaces 503. The peripheral surfaces 503 impart a square cross-sectionto the light pipe, though in other embodiments the cross-sectional shapeof the light pipe can be different, e.g., hexagonal, or octagonal.Similar to some of the previous embodiments, the peripheral surfaces 503are configured so as to reflect, via total internal reflection, thelight incident thereon. Further, similar to some of the previousembodiments, a plurality of microlenses 504 are coupled to the outputsurface 502 b to diffuse and/or redirect the light exiting the lightpipe via the output surface. Again, similar to some of the previousembodiments, in addition to or instead of the microlenses, the outputsurface 502 b can include surface texturing for diffusing the lightexiting the light pipe via the output surface. Further, similar to theprevious embodiment, a projection lens, such as a zoom lens, can beoptionally optically coupled to the microlenses 504 to receive lighttherefrom and direct the received light onto a target surface.

The input surface is optically coupled to a light source 506, which canbe, for example, a multi-color LED such as an RGBW. In this embodiment,the general direction along which the light from the light source entersthe light pipe is substantially opposite to the general direction alongwhich the light exits the light pipe via the output surface 502 b.

In some implementations, the light-mixing system 500 can transfer lightreceived at its input surface to its output surface with an efficiencyas high as about 74%, or as high as about 80%, or as high as about 90%.

In this embodiment, the input surface 502 a and the output surface 502 bare vertically separated from one another. By way of example, as shownin FIGS. 5C and 5D, the input surface 502 a and the output surface 502 bare vertically separated from one another by a distance (D). While inthis embodiment, the output surface is vertically disposed above theinput surface, in other embodiments, the output surface 502 b can bevertically positioned below the input surface.

By way of example, FIGS. 6A and 6B schematically depict anotherembodiment of the light mixing system 500 in which the output surface502 b is vertically positioned below the input surface 502 a. Ingeneral, as the length of the arcuate light-mixing waveguide between theinput and output surfaces increases, so does the light mixing capabilityof the optical system.

With reference to FIGS. 5E and 5F, in some embodiments, the light-mixingsystem 500 includes a heat sink 510 that is thermally coupled to thelight source 506 for removing heat therefrom. The heat sink 510 caninclude a plurality of fins 510 a for facilitating the removal of heatfrom the light source 506. As in this embodiment the output surface 502b of the light pipe 502 is positioned vertically above the light source506, the heat sink includes an opening 512 through which the distal endof the light pipe extends.

FIGS. 6C and 6D depict another embodiment of the light-mixing system 500in which the output surface 502 b of the light pipe 502 is positionedvertically below the input surface 502 a and a heat sink 510′ isthermally coupled to the light source 506 to facilitate the removal ofheat generated by the light source. The heat sink 510′ includes anopening 512′ that allows the passage of light exiting the light pipe 502via its output surface 502 b to the external environment.

FIG. 6E schematically depicts an embodiment of the light-mixing system500 in which a lens 520 is optically coupled to the output surface ofthe light pipe 502 to shape and/or redistribute the light rays, e.g., tofocus the light rays onto a target surface. In some embodiments, thelens 520 can be a zoom lens, e.g., a zoom lens formed by a pair oflenses having positive and negative optical powers.

By way of further illustration, FIG. 7 schematically depicts anotherembodiment of a light-mixing system 700 having a curved light pipe(light-guiding waveguide) 702 that extends from an input surface 702 a,which can receive light from a light source (not shown in this figure),to an output surface 702 b through which the light can exit the lightpipe. In this embodiment, the input and the output surfaces are placedside-by-side in close proximity to one another. In other embodiments,the light pipe can be configured such that the input and the outputsurfaces are placed side-by-side and in contact with one another. Inother words, each of the lateral and the vertical distance between theinput and the output surface can be zero.

With reference to FIGS. 8A, 8B, and 8C, in some embodiments, a lightmixing system 800 includes a light pipe 802 that extends from an inputsurface 802 a to an output surface 802 b. In this embodiment, the lightpipe 802 forms an arc such that the input and output surfaces 802 a and802 b are oriented at a 90-degree angle relative to one another. Inother words, putative vectors normal to the input and output surfaces802 a and 802 b are orthogonal to one another. Thus, the light pipe canredirect an input beam by 90 degrees to illuminate a desired targetsurface.

The input surface 802 a is optically coupled to a light source 804,which can be, for example, an LED or a combination of LEDs providinglight of different colors. The light rays entering the light pipe 802undergo total internal reflection at the peripheral surfaces of thelight pipe to reach the output surface 802 b. While in this embodimentthe light pipe has a square cross-sectional profile, in otherembodiments, it can have other cross-sectional profiles, such ashexagonal or octagonal.

In this embodiment, a plurality of microlenses 805 are optically coupledto the output surface of the light pipe 800 to redistribute and/orreshape the light as it exits the output surface. In some embodiments,the surfaces of the microlenses can be textured, for example, in amanner discussed above in connection with the previous embodiments. Byway of example, such surface texturing can be characterized by aplurality of projections having heights in a range of about 0.01 mm toabout 1 mm. In other embodiments, such surface texturing can be appliedto the output surface 802 b in absence of any microlenses. In thisembodiment, the microlenses are formed in a separate unit 807, e.g., aplastic unit, that is then coupled to the output surface 802 b. In otherembodiments, the microlenses can be incorporated into the output surface802 b.

With reference to FIGS. 8D and 8E, in some embodiments a heat sink 809can be thermally coupled to the light source 804 to remove heatgenerated by the light source. The heat sink 809 includes a plurality offins 809 a that provide a large surface area for facilitating theremoval of heat from the light source.

FIGS. 8F and 8G schematically depict that in some embodiments, aprojection lens 810 can be optically coupled to the output surface 802 bof the light pipe to project the light exiting the output surface onto atarget area. In some embodiments, the projection lens can function as azoom lens. For example, in some embodiments, the projection lens can bein the form of a lens doublet, one of which has a positive optical powerand the other a negative optical power, and can be movable relative tothe output surface 802 b so as to adjust the angular spread of a lightbeam exiting the output surface 802 b, e.g., between a narrow-beam andwide-beam angular spreads.

With reference to FIGS. 9A, 9B and 9C, in another embodiment, an opticalsystem 900 includes a light pipe 902 that extends from an input surface902 a to an output surface 902 b. In this embodiment, the light pipe isbent such that a putative vector A perpendicular to the output surface902 b forms a 45-degree angle with a putative vector A perpendicular tothe input surface 902 a. The light pipe 902 receives light from a lightsource 904 at its input surface 902 a and directs the light via totalinternal reflection at its peripheral surfaces to the output surface 902b through which the light exits the light pipe. In some embodiments, thelight source 904 can be an LED or a plurality of LEDs, e.g., LEDsproviding light of different colors.

A plurality of microlenses 905 are optically coupled to the outputsurface 902 b to redirect and/or shape the light exiting the light pipe.While in this embodiment, the microlenses 905 are formed in a separateunit 905 a that is coupled to the output surface 902 b, in otherembodiments the microlenses can be incorporated in the output surface.Further, in some embodiments, the surfaces of the microlenses can betextured, e.g., in the form of a plurality of projections having aheight in a range of about 0.01 mm to about 1 mm. In other embodiments,such surface texturing can be incorporated in the output surface 902 bin absence of the microlenses.

With reference to FIGS. 9D and 9E, in some embodiments, a heat sink 910can be thermally coupled to the light source 904 to remove heatgenerated by the light source. The heat sink 910 can include a pluralityof fins 910 a that facilitate heat removal from the light source byproviding an increased surface area.

With reference to FIGS. 9F and 9G, in some embodiments a projection lens912 can be optically coupled to the output surface 902 b to project thelight received from the light pipe onto a target surface. In someembodiments, the projection lens can be a zoom lens.

While in the above two embodiments, the input and output surfaces of thelight pipe are oriented relative to one another by 90 and 45 degrees,more generally, the input and output surfaces of the light pipe of alight-mixing system according to the present teachings can form an anglefrom 0 and 90 degrees, e.g., in a range of about 30 to 90 degrees,relative to one another. In other words, putative vectors normal to theinput and output surfaces of the light pipe can make an angle in a rangeof 0 and 90 degrees, e.g., in a range of about 30 to 90 degrees,relative to one another.

In some implementations of any of the above embodiments, the input andthe output surfaces of the light pipe of a light-mixing system accordingto the present teachings can have different surface areas. By way ofexample, as shown schematically in FIG. 8A, the output surface 802 b ofthe light pipe 802 has a surface area greater than the surface area ofthe input surface 802 a. By way of example, in some embodiments, theoutput surface can have a surface area that is at least about 10%, or atleast about 20%, or at least about 30%, or at least about 40%, or atleast about 50%, greater than the surface area of the input surface ofthe light pipe.

Further, in some implementations of any of the above embodiments, thelight pipe of a light-mixing system according to the present teachingscan have a tapered cross-sectional profile extending from the inputsurface to the output surface. By way of example, with reference to FIG.10, a light pipe 1000 exhibits a cross-sectional area that continuouslyincreases from an input surface 1002 to an output surface 1004. In otherembodiments, the cross-sectional area of a light pipe of a light-mixingsystem according to the present teachings can be uniform along thelength of the light pipe.

In some implementations of any of the above embodiments, differentportions of a light pipe of a light-mixing system according to thepresent teachings can have different cross-sectional shapes. Forexample, a portion of the light pipe can have one polygonal shape, e.g.,square, and another portion of the light pipe can have a differentpolygonal shape, e.g., hexagonal. Alternatively, a portion of the lightpipe, e.g., a proximal portion, can have a polygonal cross section andanother portion of the light pipe, e.g., a distal portion, can have around cross section. By way of example, FIG. 11 schematically depicts alight pipe 1200 having a proximal section 1200 a with a square crosssection and a distal section 1200 b having a round cross section. Inother embodiments, the light pipe can exhibit more than twocross-sectional shapes along its length.

In the above embodiments, various components of a light-mixing systemaccording to the present teachings, such as the light pipe, theprojection lens, can be formed of any suitable material. Some examplesof suitable materials include, without limitation, polymers, such asPMMA (polymethylmethacrylate) or similar polymer, silicone, glass, amongothers.

The curved light pipes in the above embodiments can advantageouslyincrease the path length of the light propagating through them, therebyenhancing light mixing, while ensuring that the height of the system canbe less than that of a conventional system providing a similar degree oflight mixing.

Those having ordinary skill in the art will appreciate that variouschanges can be made to the above embodiments without departing from thescope of the invention.

What is claimed is:
 1. A light-mixing system, comprising: a light pipecomprising: an input surface configured for receiving light from a lightsource, a light-mixing segment optically coupled to said input surface,an output surface optically coupled to said light-mixing segment throughwhich light exits the light pipe, wherein a vector normal to at leastone of said input and output surface forms a non-zero angle relative toa longitudinal axis of said light-mixing segment, and wherein said lightpipe comprises a polygonal cross section.
 2. The light pipe of claim 1,wherein said output surface comprises a plurality of microlenses fordiffusing light passing therethrough.
 3. The light pipe of claim 1,wherein said output surface comprises surface texturing.
 4. The lightpipe of claim 1, wherein said output surface comprises a plurality ofmicrolenses and surface texturing.
 5. The light pipe of claim 1, whereinsaid input surface and said output surface of the light-guidingwaveguide are substantially at the same vertical level.
 6. The lightpipe of claim 1, wherein said output surface of the light-guidingwaveguide is positioned vertically higher than said input surface. 7.The light pipe of claim 1, further comprising a projection lensoptically coupled to said output surface.
 8. The light pipe of claim 1,wherein said light source is positioned relative to said input surfaceof the light pipe such that the light entering said input surface has adirection opposite to direction of light exiting said output surface. 9.The light-mixing system of claim 1, wherein said non-zero angle is about90 degrees.
 10. The light-mixing system of claim 1, further comprising areflective surface optically coupled to said input surface and saidlight-mixing segment for directing at least a portion of the lightreceived via the input surface to said light-mixing segment.
 11. Thelight-mixing system of claim 10, wherein said reflective surface ismetalized.
 12. The light-mixing system of claim 10, wherein saidreflective surface is configured to reflect light incident thereon viatotal internal reflection.
 13. The light-mixing system of claim 1,wherein said light-mixing segment comprises a surface configured toreflect light incident thereon via total internal reflection.
 14. Thelight-mixing system of claim 1, wherein said light source comprises anLED.
 15. The light-mixing system of claim 1, wherein said light sourcecomprises a plurality of LEDs generating light of different colors. 16.The light-mixing system of claim 1, further comprising a heat sink thatis thermally coupled to the light source.
 17. The light-mixing system ofclaim 1, wherein the output surface of the light pipe has a surface areagreater than a surface area of the input surface thereof
 18. Thelight-mixing system of claim 1, wherein the light pipe has a taperedcross section extending from the input surface to the output surface.